The laces are tied from the beginning, hidden under the leg of his pants. He then has a pair of loose laces hanging out from under, making it look like there is only one and that they are untied. He then shakes his foot to disguise the retraction of the loose ones and the pulling up of his pants leg to reveal the tied ones. There is even a point where, after he has revealed the tied ones, you can see the others still hanging out at the left of the frame.
I do good?